U.S. patent application number 10/915269 was filed with the patent office on 2006-02-16 for method for exploitation of gas hydrates.
Invention is credited to Joseph A. Ayoub, Stuart I. Jardine, Terizhandur S. Ramakrishnan.
Application Number | 20060032637 10/915269 |
Document ID | / |
Family ID | 35429226 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032637 |
Kind Code |
A1 |
Ayoub; Joseph A. ; et
al. |
February 16, 2006 |
Method for exploitation of gas hydrates
Abstract
A method and apparatus for producing gas from a hydrate
formation includes the use of at least one wellbore which
penetrates the hydrate formation and further extends into an
aquifer below the hydrate formation. The aquifer provides
relatively warm water which may be produced up and into the hydrate
formation thereby causing the release of gas from the hydrate.
Suitable flow control and monitoring equipment may be included to
control the flow of water produced from the aquifer and gas
produced from the hydrate formation.
Inventors: |
Ayoub; Joseph A.; (Katy,
TX) ; Jardine; Stuart I.; (Houston, TX) ;
Ramakrishnan; Terizhandur S.; (Bethel, CT) |
Correspondence
Address: |
SCHLUMBERGER TECHNOLOGY CORPORATION
IP DEPT., WELL STIMULATION
110 SCHLUMBERGER DRIVE, MD1
SUGAR LAND
TX
77478
US
|
Family ID: |
35429226 |
Appl. No.: |
10/915269 |
Filed: |
August 10, 2004 |
Current U.S.
Class: |
166/369 ;
166/250.15 |
Current CPC
Class: |
E21B 41/0064 20130101;
E21B 43/24 20130101; Y02C 20/40 20200801; Y02C 10/14 20130101; E21B
41/0099 20200501 |
Class at
Publication: |
166/369 ;
166/250.15 |
International
Class: |
E21B 47/00 20060101
E21B047/00 |
Claims
1. A method for recovering gas from a subterranean formation having
a gas hydrate deposit located therein and wherein said formation
further includes a liquid source, comprising the steps of: (a)
providing a wellbore penetrating said gas hydrate deposit and
extending into said liquid source; and (b) producing liquid from
said liquid source into said gas hydrate deposit.
2. The method of claim 1, further comprising the step of contacting
said gas hydrate deposit with liquid from said liquid source to
produce gas.
3. The method of claim 2, further comprising the step of recovering
said gas.
4. The method of claim 1, further comprising the step of providing
a wellbore isolation mechanism positioned below said hydrate
deposit.
5. The method of claim 1, further comprising the step of providing
a wellbore isolation mechanism positioned above said hydrate
deposit.
6. The method of claim 1, wherein said wellbore is cased.
7. The method of claim 1, further comprising the step of
perforating the casing.
8. The method of claim 7, wherein perforations are placed in the
casing substantially adjacent to said liquid source.
9. The method of claim 7, wherein perforations are placed in the
casing substantially adjacent to said hydrate deposit.
10. The method of claim 9, further comprising the step of providing
a mechanism for selectively isolating said perforations.
11. The method of claim 10, wherein said mechanism is a sliding
sleeve.
12. The method of claim 4, wherein said isolation mechanism is a
valve.
13. The method of claim 5, wherein said isolation mechanism is a
valve.
14. The method of claim 3, further comprising the step of placing a
second fluid into the hydrate formation, wherein said second fluid
is capable of forming a hydrate.
15. The method of claim 14, wherein said second fluid is CO2.
16. The method of claim 1, further comprising providing at least
one sensor.
17. The method of claim 2, wherein said liquid is separated from
said gas and reinjected into said liquid source.
18. The method of claim 2, wherein said liquid is separated from
said gas and reinjected into a subterranean formation.
19. The method of claim 1, further comprising the step of
monitoring the temperature of said hydrate deposit.
20. The method of claim 1, further comprising the step of
monitoring passive seismic activity using acoustic sensors.
21. The method of either of claims 19 or 20, wherein the rate at
which liquid from the liquid source is produced into said hydrate
formation is dependent on input from said monitoring.
22. The method of either of claims 19 or 20, wherein said
monitoring is conducted from a separate wellbore.
23. A method for recovering gas from a subterranean formation
having a gas hydrate deposit located therein and further including
a liquid source, comprising the steps of: (a) providing a first
wellbore penetrating said gas hydrate deposit; (b) providing a
second wellbore penetrating said liquid source and said hydrate
deposit; (c) contacting said hydrate deposit with liquid from said
liquid source to produce a gas; and (d) recovering said gas.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a method of
producing gas from gas hydrates. More specifically, the invention
is a method for contacting a gas hydrate formation with warmer
water from an aquifer to release sequestered gas.
[0003] 2. Description of the Prior Art
[0004] A gas hydrate is a crystalline solid that consists of a gas
molecule surrounded by water molecules. The structure is similar to
ice, except that the crystalline structure is stabilized by the
presence of the gas molecule. The two molecules are dissimilar, but
mechanically intermingled, without true chemical bonding. Gas
hydrates may be formed of a number of gasses having an appropriate
molecular size. These include carbon dioxide, hydrogen sulfide and
several low-carbon-number hydrocarbons, including methane. Natural
gas hydrates are modified ice structures enclosing methane and
possibly other hydrocarbons.
[0005] Hydrates tend to form in the pore spaces of sediment layers.
However they may also be seen as nodules or deposits of pure
hydrate. Gas hydrates are stable at the temperature and pressures
typically found on the ocean floor at depths greater than about 500
m. This depth may vary depending on the conditions of a specific
location, for instance, hydrates do not tend to form until a depth
of approximately 800 m in the eastern United States. Gas hydrates
may also be stable in association with permafrost, both on- and
off-shore. Natural gas hydrates act as a gas concentrator in that
one unit volume of hydrate is equivalent to about 172 unit volumes
of methane gas at standard conditions. Often however, the hydrate
itself is dilute in the sediment, occupying 2% of the volume on
average.
[0006] Methane gas trapped in hydrates represent a huge potential
source for cleaner energy. One of the key problems in exploiting
these hydrate deposits involves finding appropriate methods to
produce and collect the gas. This invention describes a production
system that creates an appropriate completion to tap heat from an
underlying aquifer and efficiently release the gas from the hydrate
deposit to produce it to surface. In addition, it is proposed to
sequester CO.sub.2 in the form of hydrate at the same location
following the methane extraction. This process, not only serves to
sequester CO.sub.2 and help the environment, but could also be used
to stabilize the sea bed following methane extraction.
SUMMARY OF THE INVENTION
[0007] The present invention is a method of producing the gas
trapped in hydrates. The method may include single or multiple
production units aimed at releasing and collecting the gas through
the use of one or more wellbores. A typical gas collection unit may
comprise two basic configurations. The first configuration includes
a single well, which provides a water source and a conduit or
pathway for producing the gas. In this configuration, the wellbore
passes through and is completed in a hydrate zone and also extends
into a water-producing zone or aquifer. The second configuration
includes two wells. The first well extends into the water bearing
zone and provides a water source. The second well is used for
production of the gas released from the hydrate and extends into or
through the hydrate zone. In either configuration, at least one
well is drilled deeper (i.e., extending below the hydrate deposit)
and completed in an aquifer or water-producing zone below the
hydrate. In certain cases, depending on the specific nature of the
aquifer, a fracturing operation may be performed to increase flow
from the aquifer. The deeper aquifer water should be sufficiently
hot to heat the hydrate, destabilize it, and thereby cause the
release of the gas. In order to increase production, a horizontal
fracture may be formed or created in the hydrate deposit. Hydrate
deposits are typically shallow and the most likely fracture
geometry is horizontal. A horizontal fracture may be of particular
benefit to facilitate heating the hydrate by providing a larger
surface for the warm water to contact the hydrate. Where the well
is completed in the lower region of the hydrate deposit, it may be
necessary to take adequate precautions to make sure that the
hydrate in the higher regions of the deposit do not become
destabilized. For instance, monitoring of temperature through the
lateral extent of hydrate may be needed. If the temperature exceeds
a certain threshold, heating may need to be reduced or
curtailed.
[0008] Downhole production mechanisms, including valves, pipes and
sensors, allow controlled flow of the aquifer water into the
hydrate zone through the completion. This completion may include a
fracture, particularly a horizontal fracture. The production
mechanisms may also allow production of the released gas through a
completion (possibly including another horizontal hydraulic
fracture) placed higher in the hydrate zone through the same or
another vertical or horizontal wellbore. For thick hydrate deposits
(i.e., several hundred meters), several layers of
completions/horizontal fractures may initially be used in order to
efficiently release and collect the gas. For thinner hydrate
deposits a single completion/horizontal fracture may be created
towards the upper part of the hydrate deposit. The production
mechanisms installed may further be used to alternate between the
flow of water from the warm aquifer and production of released gas
to surface. In certain cases, it may be beneficial to produce the
water injected into the hydrate zone along with the released gas
and replenish the hydrate zone with fresh warm water from the
aquifer. The produced water can be either reinjected into an
aquifer or disposed off appropriately.
[0009] Any number of sensors may be deployed to track downhole
performance via measurements of temperature, pressure and flow
rates within the production well or in separate monitoring wells.
For instance, temperature may be monitored through side track wells
to ensure that the upper portions of the hydrate layer both near
and away from the production well do not decompose, in order to
prevent methane leakage to the atmosphere. Gas and acoustic
detectors may also be used. The input from the sensors can guide
the activation of the appropriate downhole valve to control the
heating of the sediment by adjusting the water injection. The
producing wells are typically tied to a large pipeline that
conducts the produced gas towards a compressor station and onward
for further processing/distribution. For hydrate formed in
sediments, the fractures could enhance significantly the production
process. Since constant heating of the hydrate layer may be needed
the water injected into the hydrate may have to be produced
periodically, and replenished with fresh warm water from the
aquifer below.
[0010] In addition, the gas hydrate wells may be used to sequester
CO.sub.2 as hydrate by injecting the CO.sub.2 down the well and
into the previously depleted methane hydrate zone. CO.sub.2 and
methane hydrates can form under similar pressure/temperature and
water conditions. The downhole temperature and pressure needed for
CO.sub.2 hydrate formation are typically evaluated to ensure that
CO.sub.2 hydrate formation is possible. If so, the installed
production mechanisms may be used to inject the CO.sub.2, which is
typically in a liquid form, into the formation where it mixes with
in situ water and forms hydrate.
[0011] The CO.sub.2 sequestration process described above would not
only address a very contemporary environmental concern, but could
also serve to stabilize/reinforce the downhole structure. It is
well known that some hydrate deposits under the sea floor carry a
high risk of causing destabilization of the sea floor. The proposed
CO.sub.2 sequestration process provides a solution by replacing the
methane hydrate and reinforcing the existing structure. Acoustic
detectors could be used to help predict any impending formation
instabilities and decide when to initiate the switch from methane
production to CO.sub.2 sequestration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram of a single wellbore embodiment of the
present invention.
[0013] FIG. 2 is a diagram of a multiple wellbore embodiment of the
present invention.
[0014] FIG. 3 is a diagram showing a wellbore configuration for
reinjecting produced water.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention is a method for producing gas from gas
hydrate formations using relatively warmer water from an aquifer or
other water-producing formation or zone below the hydrate
formation.
[0016] FIG. 1 shows a first embodiment of the invention, wherein a
single cased wellbore 10 is used to produce water from an aquifer
12 or other water-producing formation or zone and to produce gas
generated from a gas hydrate formation 14. The wellbore extends
through the gas hydrate formation and into the aquifer. Said
aquifer is preferably located or positioned substantially below
(i.e., deeper) than the hydrate formation. Depending on the
specific features of the aquifer, it may be desirable to perform a
stimulation operation to increase water output. This may involve
hydraulic fracturing, acidizing or the like. Similarly, it may also
be desirable to fracture the hydrate deposit prior to treatment
with water from the aquifer. Where necessary, the aquifer water may
be suitable pressurized using a suitable pumping device.
[0017] Once the wellbore is completed in the aquifer, water may be
produced up into the gas hydrate formation. The influx of
relatively warmer water from the aquifer results in a release of
the gas trapped or sequestered in the hydrate. The injected water
may cool relatively rapidly, and therefore it is preferable to
produce the injected water and reinject fresh hot water. The
produced water may have methane liberated in or with the water.
This comingled water and gas may be separated either in situ or on
the surface. The separated water may be reinjected into the hydrate
layer, the aquifer or an alternate storage location, such as an
alternate aquifer. Any suitable arrangement of valves 18 or other
wellbore flow control equipment or devices may be used to control
the flow of water from the aquifer 12 into the hydrate formation
14. Flapper valves, ball valves and formation isolation valves
(such as those described in U.S. Pat. Nos. 6,352,119 and 6,691,785,
both which are incorporated herein by reference) are preferred. In
a particularly preferred embodiment, the valve system 18 is
selectively controlled from the surface by a suitable control
system. This control system may include an electrical or hydraulic
communication system such as wires or lines 20 extending from the
surface to the valves. The control system may also include any
suitable wireless technology.
[0018] In addition to providing a mechanism for selectively
controlling the flow of water from the aquifer, it may also be
desirable to provide a fail-safe mechanism for preventing the flow
of water and/or gas through the wellbore to the surface, or flow of
sea water into the wellbore in case of accidental failure of well
surface equipment. Such mechanism may be any suitable device;
however, a valve-based system 30 is preferred. More particularly,
flapper valves, ball valves and formation isolation valves are
preferred. In an alternative embodiment, the BOPs may be used to
prevent flow or production of wellbore fluids to the surface.
[0019] As shown in FIG. 1, the casing 22 must be perforated in
order to establish fluid communication between the wellbore and the
hydrate formation. Depending on the size of hydrate formation, it
may be useful or desirable to place or locate perforations in
multiple locations in the formation 24, 25, 26. Once the
perforations are formed in the casing, the hydrate formation may
also be fractured or otherwise treated. In order to selectively
choose the locations and timing of water injection and the location
and timing of gas production an internal isolation mechanism 28 may
be included to seal or obstruct the perforations. In a preferred
embodiment, a sliding sleeve mechanism may be used to selectively
open or isolate the perforations. In an alternative embodiment, a
chemical isolation mechanism may be used to seal the perforations.
Such chemical isolation mechanism may include a cement or polymer
based material or any other material suitable for substantially
preventing or limiting the flow of fluids into or out of the
perforations.
[0020] A sensor package including but not limited to, temperature
sensors (e.g., Schlumberger's Distributed Temperature System (DTS)
as described in U.S. Pat. No. 5,286,109 which is incorporated
herein by reference), pressure sensors, gas detectors and acoustic
sensors (e.g., geophones) may be deployed to monitor the water
flood process and trigger the activation of any of the downhole
control valves and equipment required to adequately control the
treatment of the hydrate formation. For example, shutting off or
reducing the water injection into the hydrate and opening a sliding
sleeve or other valve to start gas production. A separate well
could also be used to monitor temperature or passive seismic events
away from the producing well to better control the production
process and avoid destabilizing the hydrate zone.
[0021] In another embodiment of the present invention, and as shown
in FIG. 2, a first wellbore 100 is provided which extends from the
surface 102 through a gas hydrate formation 104 and into an aquifer
or water-bearing formation or zone 106. A second wellbore 108
extends from the surface 102 and into the gas hydrate formation
104. The first wellbore provides fluid communication between the
aquifer and the gas hydrate, allowing water produced from the
aquifer to contact the gas hydrate. Preferably, the first wellbore
is sealed or isolated from the surface (above the level of the
hydrate formation) to prevent either water or gas from being
conducted or produced to the surface. Alternatively, water and/or
gas may be produced from the first wellbore, followed by water
injection into the hydrate zone, until communication is established
with the second wellbore. Once such communication is established,
the first wellbore may then be isolated from the surface.
Preferably, a valve system 110 is used to provide isolation of the
aquifer, if needed. Valves useful in the present invention, include
but are not limited to, flapper valves, ball valves and formation
isolation valves. In a preferred embodiment, a suitable arrangement
of flow control mechanisms (such as valves or flappers) may be used
to provide water to the hydrate formation, produce and separate the
gas and then reinject the water into an aquifer. This embodiment is
particularly useful where continued melting of the hydrate does not
occur.
[0022] As water from the aquifer contacts the hydrate, gas is
released. This released gas, along with water, may be produced or
conducted to the surface through the second wellbore. The second
wellbore may include any number of suitable flow control and
measurement mechanisms. Preferably, the second wellbore will
include at least one valve apparatus or system 112 for controlling
the flow of produced fluids from the formation to the surface.
[0023] In yet another embodiment of the present invention, and as
shown in FIG. 3, a wellbore 200 may be provided which extends from
the surface 202 through a hydrate formation or deposit 204 and into
an aquifer or other water bearing formation 206. The wellbore
contains or has disposed therein a conduit 208 extending from the
surface to the aquifer. The conduit may be any suitable material,
including drill string, casing or coiled tubing. A first flow
control mechanism 210 is positioned below the hydrate formation and
above the aquifer to control the flow of water from the aquifer to
the formation. This mechanism may include any suitable device or
material, but is preferably a valve. More preferably the valve can
be controlled from the surface by an operator. A second flow
control mechanism 212 is positioned substantially adjacent to the
region or zone within the hydrate formation that is to be treated
or contacted with water from the aquifer. In a preferred
embodiment, the second flow control mechanism is a sliding sleeve;
however, it should be understood that any suitable device may be
used. The sliding sleeve may be selectively opened and closed by
the operator. Depending on the specific nature of the hydrate
formation and the treatment parameters, any number of flow control
mechanisms may be positioned within the hydrate formation, each
corresponding generally to a region or zone to be treated.
[0024] As the first valve 210 is opened and water from the aquifer
flows upward, the sliding sleeve 212 may be opened to allow the
water to contact the hydrate. As gas is produced it flows upward to
the surface, along with water from the aquifer. At the surface, the
water and gas may be separated. In certain cases, it may be
desireable to reinject the separated water back into the aquifer
used for production or another aquifer using a separate well or the
same wellbore. In such a case, the sliding sleeve(s) may be moved
to a closed position to prevent the separated water from entering
the hydrate formation as it is reinjected down or through the
conduit. Alternatively, a second conduit 214 may be provided to
allow the water to be reinjected into the aquifer. In this way,
water and gas are produced to the surface through the first conduit
and water is reinjected through the second. Therefore, production
does not have to be interrupted to reinject the separated water.
Where a plurality of zones are being treated in the hydrate
formation, it may be desireable to selectively treat a lower zone,
followed by an upper zone. The operator controlled flow control
device(s) 212 allow selective treatment of specific zones.
[0025] As hydrate is converted to gas, the area around the hydrate
deposit, as well as the deposit itself, may be destabilized. Where
the risk of destabilization is present, it may be desirable to
design or arrange wellbore(s) to minimize this risk. For instance,
pockets in the hydrate deposit may be selectively produced such
that the produced pockets are spaced far enough from each other
such that the hydrate deposit remain stable. Alternatively, a
network or wellbores and/or pipelines may be put in place to reduce
or minimize the subsidence effects of hydrate production or
removal. To prevent complete destabilization, temperature
monitoring wells may be created on the upper portion of the hydrate
deposit. As the temperature changes, water flow may be adjusted to
produce controlled heating of the hydrate layer.
[0026] In another embodiment of the present invention, CO.sub.2 may
be injected or otherwise placed into the hydrate formation to
effectively replace the methane which is produced. In this way, the
CO.sub.2 may be stored or otherwise disposed of and may also serve
to stabilize the hydrate formation following removal of the
methane. Preferably, the CO.sub.2 is provided in a liquid form,
mixed with water and injected into the hydrate layer. More
preferably, the CO.sub.2 is provided in supercritical form.
[0027] The CO.sub.2 may be placed using the same wellbore(s) used
to produce methane from the hydrate formation. Alternatively,
additional wellbores may be provided, depending on the specific
nature of operation being conducted. For instance, in one
embodiment, methane may be produced from a first wellbore. Upon
completion of the methane production operation, CO.sub.2 may be
injected down the same wellbore. In another embodiment, a first
wellbore may initially be used to produce water from the aquifer
into the hydrate formation. A second wellbore may be used to
produce the methane to the surface. This first wellbore may be used
to place CO.sub.2 into the hydrate formation once a sufficient
quantity of water has been provided to the formation.
[0028] In an alternative embodiment, the CO.sub.2 may be provided
or placed into the hydrate formation through coiled tubing. The
tubing may be run into the wellbore and positioned substantially
adjacent to the hydrate formation. Suitable wellbore isolation
mechanisms, such as packers, may be used to prevent the CO.sub.2
from migrating out of or away from the hydrate formation. The
CO.sub.2 may also be mixed with the water and injected.
[0029] These specific embodiments should not limit the scope of the
present invention, as any suitable configuration of equipment may
be used.
* * * * *